Solid polymer dispersions and method for their preparation

ABSTRACT

Solid blends of rubbery polymers and amorphous or crystalline polymers, said blends being free-flowing at temperatures lower than the glass transition temperature or crystalline melting temperature of the amorphous or crystalline polymer, are prepared by intimate mixing procedures. In general, said mixing conditions include high shear conditions sufficient to convert polymer A to dispersed particles coated with polymer B and produce a free-flowing powder blend.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.09/696,088, filed Oct. 26, 2000, now ABN which in turn is a division ofapplication Ser. No. 09/218,925, filed Dec. 22, 1998, now U.S. Pat. No.6,194,518, which in turn is a continuation-in-part of application Ser.No. 08/959,256, filed Oct. 29, 1997, now abandoned, which in turn is acontinuation-in-part of application Ser. No. 08/742,536, filed Nov. 1,1996, now abandoned, which are incorporated herein by reference.

BACKGROUND OF INVENTION

This invention relates to polymer dispersions in solid form and a methodfor their preparation. More particularly, it relates to the preparationof polymer blends in solid form.

The use of elastomeric (i.e., rubbery) polymers as additives in blendscomprising other polymers is known. Various rubbery polymers are usefulas impact modifiers, flame retardants and additives conferring otherproperties on blends in which they are incorporated. While thedispersion of liquid additives in polymeric powders is well known andpreviously documented by Dahms et al. (U.S. Pat. No. 3,301,813), auniform and fine dispersion of rubbery polymers in thermoplastics toform dry free-flowing powders has not been reported.

U.S. Pat. Nos. 3,824,208, 5,153,238, 5,391,594 and 5,412,014 describethe incorporation of fillers such as silica in rubbery polymers to formcompositions which exist as free-flowing particles. However, it issometimes highly desirable to exclude inorganic materials such as silicafrom polymer blends or coat the surface of the silica particles withsiloxane elastomers, in which case these compositions are no longerfree-flowing. The surface chemistry of the filler in some cases canresult in degradation of the matrix polymer.

Conventional approaches for obtaining free-flowing powders withelastomeric components include the use of block copolymers, core-shellcopolymers or graft copolymers with thermoplastics. Copolymerization orgrafting of glassy/crystalline thermoplastic prevents agglomeration ofthe rubbery component and enables convenient addition of these impactmodifiers as free-flowing powders in extrusion equipment for meltprocessing. Such approaches however do not provide a cost effectivesolution for preparing free-flowing polymeric dispersions.

It is difficult, however, to prepare homogeneous blends of rubberypolymers with other resins, owing to the relative intractabilities ofsaid rubbery polymers and the slow progress of dispersion of saidpolymer in the blend. Examples of some alternative approaches forobtaining free-flowing powders include mixing a dispersion of an organicthermoplastic polymer with an emulsion of a silicone resin as taught byFuhr et al. in U.S. Pat. No. 5,100,958. This method is once again notcost effective since it involves a subsequent adjustment of pH forcoagulation followed by isolation and drying of the coagulate. Anothermethod proposed by Vaughn in U.S. Pat. No. 4,153,639 involves mixing theresin and the rubbery additive (in this case silicone gum) in a liquidmedium having a component which vaporizes readily. The liquid medium iscontacted with flowing live steam in a conduit and the mixture is fedinto a closed chamber from which the superheated, vaporized liquidcomponents are removed and a particulate blend is extracted.

Other practical limitations in melt—melt blending of thermoplastics withrubbery polymers include the inability to disperse the rubber phaseadequately in the thermoplastic melt using the conventional processingequipment due to excessive shear heating in the extruders and amorphological balance between drop break up (dispersion) and thesubsequent coalescence of the dispersed particles.

Some applications like powder coating require the availability of thethermoplastic resin blend in a powdery form. One route for the formationof thermoplastic blend powders involves high temperature melt extrusionof the various melt components followed by grinding of the thermoplasticpellets to obtain a free-flowing powder. The ability to directly formuniform thermoplastic blends with fine morphologies at lower processingtemperatures can provide a direct, cost-effective and simpler process.

SUMMARY OF INVENTION

The present invention facilitates the formation of polymer blends asdescribed herein above. In particular, it makes it possible to prepareblends which are solid and free-flowing, said blends comprising high andoften major proportions of rubbery materials such as polyorganosiloxanesand synthetic elastomers, said blends also containing another resinousconstituent. Among the blends that can be produced are those useful asproducts in their own right and those useful as master batches suitablefor incorporation as additives in other polymer compositions.

In one of its aspects, the present invention provides a method forpreparing a blend, said blend comprising: a polyorganosiloxane (A)having at least one of a glass transition temperature (Tg_(a)) or amelting temperature (Tm_(a)), a polyphenylene ether (B) having at leastone of a glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,which comprises intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend, said blend being free of silica filler and treatedsilica filler. Also provided is a composition prepared by theaforementioned method.

DETAILED DESCRIPTION

In some embodiments the present invention provides a method whereinTg_(a) is below about 160° C., in other embodiments below about 50° C.,and in still other embodiments below about minus 100° C. In someembodiments the present invention provides a method wherein polymer B iscrystalline. In still other embodiments the present invention provides amethod wherein polymer B is amorphous and Tg_(b) is above about 100° C.It is generally known to those skilled in the art that many, but notall, polymers as commonly obtained comprise a mixture of amorphous andcrystalline fractions. In some particular polymers an amorphous phasepredominates, while in other particular polymers a crystalline phase mayprovide a significant fraction of the total polymer. In other particularembodiments polymer A and polymer B are typically immiscible andincompatible with each other.

In various embodiments the present invention provides a method whereinpolymer A is a polyorganosiloxane, an ethylene-propylene rubber,polybutadiene, polyisoprene, neoprene, an acrylic rubber, or copolymersthereof, and polymer B is an olefin polymer, a polycarbonate, poly(vinylchloride), a linear polyester, a vinyl aromatic polymer, a polyphenyleneether, a polyimide, a polyethersulfone, a polyetherketone, a polyarylenesulfide, or copolymers thereof. In particular embodiments the presentinvention provides a method wherein polymer B ispoly(2,6-dimethyl-1,4-phenylene ether), poly(butylene terephthalate), orpolyetherimide.

Provided in yet another embodiment is a method wherein polymers A and Bare mixed in a rotary blade mixer at a blade tip velocity in the rangeof about 1,000-15,000 cm/sec.

In another embodiment the instant invention provides a compositioncomprising a blend of polymer A having glass transition temperature(Tg_(a)) and/or a melting temperature (Tm_(a)), polymer B having glasstransition temperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, said composition beingproduced by the process of intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a)and Tm_(a) and the higher ofTg_(b) and Tm_(b), for a time and under shear conditions sufficient toconvert polymer A to dispersed particles coated with polymer B andproduce a free-flowing blend in the form of a powder. In still anotherembodiment the instant invention provides a composition comprising ablend of polymer A having glass transition temperature (Tg_(a)) and/or amelting temperature (Tm_(a)), polymer B having glass transitiontemperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, said composition beingproduced by the process of intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a), and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce afree-flowing blend in the form of a powder. In some particularembodiments the free-flowing blend is prepared by the method of theinvention which does not involve melting of polymer B. In otherparticular embodiments polymer B may be plasticized, for example bymixing with at least one other polymer or additive which is at leastpartly miscible with polymer B such that the Tg of the mixture is lowerthan the Tg of polymer B itself, in which case the temperature range forpreparing blends by the present method is at a suitable temperaturebetween the lower of Tg_(a) and Tm_(a), and the value of Tg for themixture of polymer B with at least one other polymer or additive whichis at least partly miscible with polymer B. An example of a plasticizedmixture of a polymer B is a mixture of a polyphenylene ether such aspoly-2,6-dimethyl-1,4-phenylene ether with a polystyrene, which mixturetypically has a Tg in between that of the polyphenylene ether and thepolystyrene dependent upon, among other factors, the relativeproportions of the two polymers in the mixture.

The free-flowing powders prepared by the method of the present inventionhave a mean particle size in one embodiment in a range of between about50 microns and about 4000 microns, in another embodiment in a range ofbetween about 100 microns and about 3000 microns, in another embodimentin a range of between about 200 microns and about 2000 microns, inanother embodiment in a range of between about 200 microns and about1500 microns, in another embodiment in a range of between about 250microns and about 1200 microns, in another embodiment in a range ofbetween about 300 microns and about 1000 microns, and in still anotherembodiment in a range of between about 400 microns and about 900microns. In a particular embodiment a free flowing powder blend may bedistinguished from a pelletized extrudate made in a melt process whichpellets typically have at least one dimension greater than about 4000microns.

In some embodiments the present invention provides a composition whereinTg_(a) is below about 160° C., in other embodiments below about 50° C.,and in still other embodiments below about minus 100° C. In someembodiments the present invention provides a composition wherein polymerB is crystalline. In still other embodiments the present inventionprovides a composition wherein polymer B is amorphous and Tg_(b) isabove about 100° C.

In various embodiments the present invention provides a compositionwherein polymer A is a polyorganosiloxane, an ethylene-propylene rubber,polybutadiene, polyisoprene, neoprene, an acrylic rubber, or copolymersthereof, and polymer B is an olefin polymer, a polycarbonate, poly(vinylchloride), a linear polyester, a vinyl aromatic polymer, a polyphenyleneether, a polyimide, a. polyethersulfone, a polyetherketone, apolyarylene sulfide, or copolymers thereof. In particular embodimentsthe present invention provides a composition wherein polymer B ispoly(2,6-dimethyl-1,4-phenylene ether), poly(butylene terephthalate), orpolyetherimide.

Elastomeric examples of polymer A employed according to the presentinvention are those which have a relatively low glass transitiontemperature Tg_(a). The value of Tg_(a) is generally below about 25° C.and may be below 0° C. For example, polydiorganosiloxane gums useful inthe invention may have Tg values down to about minus 127° C. with amelting point of about minus 40° C. Polymer A typically has a highviscosity, most often in the range of about 500,000 to about 20,000,000centipoise at a shear rate on the order of 10 sec-⁻¹, however polymershaving viscosities as low as 5,000 and above about 20,000,000 may alsobe used. In some embodiments examples of polymer A have a number averagemolecular weight of greater than about 10,000 and in other embodimentsgreater than about 20,000.

In various embodiments polymer A comprises at least onepolyorganosiloxane, especially polydialkylsiloxanes such aspolydimethylsiloxane and their fluorinated derivatives such aspoly(trifluoropropylmethylsiloxane). However, other rubbery polymersincluding ethylene-propylene rubbers, polybutadiene, polyisoprene,neoprene (polychloroprene) and acrylic rubbers, such as poly(ethylacrylate), poly(isobutyl acrylate) and poly(n-butyl acrylate) orcopolymers thereof may also be employed.

Polymers useful as polymer B may be amorphous or crystalline. Whenamorphous, they are characterized by their Tg_(b) value; whencrystalline, the crystalline melting temperature (Tm_(b)) may be moresignificant. Thus, there is a temperature span which is above the glasstransition temperature (Tg_(a)) or melting point (Tm_(a)) of polymer Aand below the higher of the glass transition temperature (Tg_(b)) orcrystalline melting temperature (Tm_(b)) of polymer B.

Illustrative polymers useful as polymer B include olefin polymers suchas polyethylene and polypropylene, polycarbonates, poly(vinyl chloride),linear polyesters such as poly(ethylene terephthalate) and poly(butyleneterephthalate), vinylaromatic polymers including polystyrene andstyrene-acrylonitrile copolymers, polyphenylene ethers, polyimides(including polyetherimides), polyethersulfones, polyetherketones andpolyarylene sulfides. In some embodiments polymers useful as polymer Bare those having glass transition temperatures above about 150° C. Inparticular embodiments polymers useful as polymer B comprisepolyphenylene ethers, such as, but not limited to,poly(2,6-dimethyl-1,4-phenylene ether) and poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether).

The compositions of the invention may include additives such as fillers,plasticizers, compatibilizers, lubricants, UV screeners, flameretardants, antistatic agents, antioxidants, and the like. In particularembodiments compositions exclude inorganic fillers such as silica fillerand treated silica filler.

In a particular embodiment of the invention, polymers A and B are mixedunder high shear conditions, at a temperature higher than Tg_(a) orTm_(a) and lower than the higher of Tg_(b) and Tm_(b). In anotherparticular embodiment of the invention, polymers A and B are mixed underhigh shear conditions, at a temperature higher than Tg_(a) or Tm_(a) andlower than the value of Tg_(b). Mixing is generally conducted in one ormore discrete steps rather than continuously as in an extruder, andunder high shear conditions sufficient to produce a composition of thetype described hereinafter. High shear mixers of this type are known inthe art and include Waring blenders, Henschel mixers, Drais mixers andmixer-granulators of the type manufactured by Littleford Bros.,Florence, Ky.

In general, both polymers are charged in their entirety before mixingbegins. It is within the scope of the invention, however, to add polymerA and polymer B incrementally, so as to maintain conditions under whicha dispersion of polymer A in solid polymer B is formed.

It has been shown that initially, a dispersion of gum (polymer A) insolid (polymer B) is formed. During the high shear mixing process, aprogressive breakdown of the particle size of polymer A occurs.Simultaneously, the particles of polymer B coat those of polymer A toform a solid, particulate blend which is a solid dispersion of polymer Ain polymer B and which is free-flowing at temperatures below the higherof Tg_(b) and Tm_(b).

The proportions of polymers A and B, as well as the mixing time andconditions, are chosen to ensure that all particles of polymer A aredispersed and coated. If the mixing time is too long, polymer A willform particles so small that the quantity of polymer B will beinadequate to fully coat them, whereupon reagglomeration will take placeimmediately or upon storage.

Thus, suitable proportions and mixing conditions can be determined bysimple experimentation. Weight ratios of polymer B to polymer A are invarious embodiments in the range of about 1:1 to about 5:1. In the caseof a rotary blade mixer, blade tip velocities in the range of about1,500 to about 15,000 cm/sec are generally adequate to produce therequired high shear mixing.

The blending temperature is not particularly critical. In one embodimentthe blending temperature is between the lower of Tg_(a) and Tm_(a) andthe higher of Tg_(b) and Tm_(b). In another embodiment the blendingtemperature is between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b). In a particular embodiment where Tg_(a) is below about andTg_(b) or Tm_(b) is above about 150° C., blending at moderatetemperatures in the range of about 20° C. to about 75° C., andespecially at ambient temperature of about 25° C., is satisfactory. Inother embodiments, polyethylene with a Tm of about 10° C. may beemployed as polymer A with a polyphenylene ether having a Tg of 210° C.as polymer B, if blending is at a temperature typically around 150° C.In various embodiments the blending temperature is below both Tg_(b) andTm_(b).

Following the blending operation of the present invention, it issometimes desirable to extrude and to pelletize the polymer blend of theinvention to form a storable material. Depending on the constituentsemployed, this storable material may itself be a useful polymercomposition or may be a master batch or an additive for incorporationinto other polymer compositions.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The following examples are included to provideadditional guidance to those skilled in the art in practicing theclaimed invention. The examples provided are merely representative ofthe work that contributes to the teaching of the present application.Accordingly, these examples are not intended to limit the invention, asdefined in the appended claims, in any manner. All parts are by weight.

EXAMPLE 1

A mixture of 25 parts of a vinyl-terminated polydimethylsiloxane gum (Tgabout minus 127° C. & Tm about minus 40° C.) having a viscosity of about3.9 million centipoise at a shear rate of about 10.14 sec-⁻¹ and 100parts of a poly(2,6-dimethyl-1,4-phenylene ether) having a Tg_(b) ofabout 210° C. having an intrinsic viscosity of 0.4 dl/g (in chloroformat 25° C.) was mixed at room temperature (about 25° C.) in a

Waring blender at high speed for 10 minutes. The desired blend wasobtained as a free-flowing powder, with 2.36 parts of unblended siliconeremaining. The blend was capable of being molded, as shown by acompression molding operation at 300° C. Mixing time and shear rate arecritical for controlling the amount of unblended silicone.

EXAMPLE 2

The procedure of Example 1 was repeated, except that mixing wasconducted in a Henschel mixer at a tip speed of 4,000 cm/s and ambienttemperature. The product was a free-flowing powder capable of extrusionand molding with no detectable unblended silicone.

EXAMPLE 3

The procedure of Example 2 was employed to prepare a free-flowing powderof 4 parts of polyethylene powder (Tm_(b) about 120° C., and Tg_(b)about minus 80° C.) and part of methyl-stopped polydimethylsiloxane gum(Tg about minus 127° C. & Tm about minus 40° C.) having a viscosity ofabout 3,900,000 centipoise at 10.14 sec-⁻¹. The blend was capable ofextrusion and molding.

EXAMPLE 4

The procedure of Example 3 was repeated, substituting 4 parts ofpolystyrene powder (Tg_(b) about 100° C.) for the polyethylene powder. Asimilar product was obtained.

EXAMPLE 5

The procedure of Example 4 was repeated, substituting 4 parts ofbisphenol A polycarbonate powder (Tg_(b) about 162° C.) for thepolyethylene powder. A similar product was obtained.

EXAMPLE 6

The procedure of Example 1 was repeated, using a blend of 1 part each ofthe polyphenylene ether (Tg_(b) about 210° C.) and an ethylene-propylenerubber (Tg_(a) about minus 80° C.). A well dispersed, free-flowingpowder with a shelf life of at least one month was obtained. The blendwas capable of extrusion and molding.

While the invention has been illustrated and described in typicalembodiments, it is not intended to be limited to the details shown,since various modifications and substitutions can be made withoutdeparting in any way from the spirit of the present invention. As such,further modifications and equivalents of the invention herein disclosedmay occur to persons skilled in the art using no more than routineexperimentation, and all such modifications and equivalents are believedto be within the spirit and scope of the invention as defined by thefollowing claims. All U.S. Patents and U.S. Patent applications citedherein are incorporated herein by reference.

What is claimed is:
 1. A method for preparing a blend, said blendcomprising: a polyorganosiloxane (A) having at least one of a glasstransition temperature (Tg_(a)) or a melting temperature (Tm_(a)), apolyphenylene ether (B) having at least one of a glass transitiontemperature (Tg_(b)) or melting temperature (Tm_(b)), whereinTg_(a)<Tg_(b) when polymers A and B are amorphous, Tm_(a)<Tm_(b) whenboth polymers A and B are crystalline, Tg_(a)<Tm_(b) when polymer A isamorphous and polymer B is crystalline, and Tm_(a)<Tg_(b) when polymer Ais crystalline and polymer B is amorphous, which comprises intimatelymixing said polymers at a suitable temperature between the lower ofTg_(a) and Tm_(a) and the value of Tg_(b), for a time and under shearconditions sufficient to convert polymer A to dispersed particles coatedwith polymer B and produce a blend in the form of a free-flowing powder,said blend being free of silica filler and treated silica filler.
 2. Themethod according to claim 1 wherein Tg_(a) is below about 160° C.
 3. Themethod according to claim 2 wherein Tg_(a) is below about 50° C.
 4. Themethod according to claim 3 wherein Tg_(a) is below about minus 100° C.5. The method according to claim 2 wherein polymer B is crystalline. 6.The method according to claim 3 wherein polymer B is amorphous andTg_(b) is above about 100° C.
 7. The method according to claim 1 whereinthe polyorganosiloxane comprises a polydimethylsiloxane.
 8. The methodaccording to claim 1 wherein the polyphenylene ether (B) comprises apoly(2,6-dimethyl-1,4-phenylene ether).
 9. The method according to claim1 wherein said polymers are mixed in a rotary blade mixer at a blade tipvelocity in the range of about 1,000 to about 15,000 cm/sec.
 10. Themethod of claim 1 wherein the polyorganosiloxane has a viscosity in arange between 5,000 and about 20,000,000 centipoise at a shear rate ofabout 10 sec⁻¹.
 11. A method for preparing a blend, said blendconsisting essentially of: a polyorganosiloxane (A) having at least oneof a glass transition temperature (Tg_(a)) or a melting temperature(Tm_(a)), a poly-2,6-dimethyl-1,4-phenylene ether (B) having at leastone of a glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,which comprises intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce ablend in the form of a free-flowing powder having a mean particle sizein a range of between about 50 microns and about 4000 microns, saidblend being free of silica filler and treated silica filler, and whereinweight ratios of polymer B to polymer A are in the range of about 1:1 toabout 5:1.
 12. A composition comprising a blend of: a polyorganosiloxane(A) having at least one of a glass transition temperature (Tg_(a)) or amelting temperature (Tm_(a)), a polyphenylene ether (B) having at leastone of a glass transition temperature (Tg_(b)) or melting temperature(Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A and B are amorphous,Tm_(a)<Tm_(b) when both polymers A and B are crystalline, Tg_(a)<Tm_(b)when polymer A is amorphous and polymer B is crystalline, andTm_(a)<Tg_(b) when polymer A is crystalline and polymer B is amorphous,produced by the process of intimately mixing said polymers at a suitabletemperature between the lower of Tg_(a) and Tm_(a) and the value ofTg_(b), for a time and under shear conditions sufficient to convertpolymer A to dispersed particles coated with polymer B and produce ablend in the form of a free-flowing powder, said composition being freeof silica filler and treated silica filler.
 13. The compositionaccording to claim 12 wherein Tg_(a) is below about 160° C.
 14. Thecomposition according to claim 13 wherein Tg_(a) is below about 50° C.15. The composition according to claim 14 wherein the Tg_(a) is belowabout minus 100° C.
 16. The composition according to claim 12 whereinpolymer B is crystalline.
 17. The composition according to claim 14wherein polymer B is amorphous and Tg_(b) is above about 100° C.
 18. Thecomposition according to claim 12 wherein the polyorganosiloxanecomprises a polydimethylsiloxane.
 19. The composition according to claim12 wherein the polyphenylene ether (B) comprises apoly(2,6-dimethyl-1,4-phenylene ether).
 20. The composition of claim 12wherein said polymers are mixed in a rotary blade mixer at a blade tipvelocity in the range of about 1,000 to about 15,000 cm/sec.
 21. Thecomposition of claim 12 wherein the polyorganosiloxane has a viscosityin a range between 5,000 and about 20,000,000 centipoise at a shear rateof about 10 sec⁻¹.
 22. A composition consisting essentially of a blendof: a polyorganosiloxane (A) having at least one of a glass transitiontemperature (Tg_(a)) or a melting temperature (Tm_(a)), apoly-2,6-dimethyl-1,4-phenylene ether (B) having at least one of a glasstransition temperature glass transition temperature (Tg_(b)) or amelting temperature (Tm_(b)), wherein Tg_(a)<Tg_(b) when polymers A andB are amorphous, Tm_(a)<Tm_(b) when both polymers A and B arecrystalline, Tg_(a)<Tm_(b) when polymer A is amorphous and polymer B iscrystalline, and Tm_(a)<Tg_(b) when polymer A is crystalline and polymerB is amorphous, produced by the process of intimately mixing saidpolymers at a suitable temperature between the lower of Tg_(a) andTm_(a) and the value of Tg_(b), for a time and under shear conditionssufficient to convert polymer A to dispersed particles coated withpolymer B and produce a blend in the form of a free-flowing powderhaving a mean particle size in a range of between about 50 microns andabout 4000 microns, said composition being free of silica filler andtreated silica filler, and wherein weight ratios of polymer B to polymerA are in the range of about 1:1 to about 5:1.
 23. The method accordingto claim 1 wherein said powder has a mean particle size in a range ofbetween about 50 microns and about 4000 microns.
 24. The compositionaccording to claim 12 wherein said powder has a mean particle size in arange of between about 50 microns and about 4000 microns.
 25. The methodaccording to claim 1 wherein weight ratios of polymer B to polymer A arein the range of about 1:1 to about 5:1.
 26. The composition according toclaim 12 wherein weight ratios of polymer B to polymer A in the range ofabout 1:1 to about 5:1.